Hydraulic circuit for a hydraulic excavator

ABSTRACT

A hydraulic circuit for a hydraulic excavator having a motor drive which acts on at least two closed drive circuits which are connected in parallel, each have a hydraulic pump and a hydraulic motor and which operate on a common output drive, connecting lines being provided between the hydraulic pump and the hydraulic motor of a respective drive circuit, is intended to be improved such that mutual contamination of the components of different driving means with particles in the event of damage is largely avoided and it is also made easier to ascertain the damage. 
     This is achieved by the connecting lines (L 11 , L 12 ; L 21 , L 22 ) of each drive circuit (A 1 , A 2 ) being arranged only between the hydraulic pump (P 1 , P 2 ) and the hydraulic motor (HM 1 , HM 2 ) of the respective drive circuit (A 1 , A 2 ) in such a way that there is no hydraulic connection between the different drive circuits (A 1 , A 2 ), the respective drive circuit (A 1 , A 2 ) each having its own control valve (S 1 , S 2 ) connected to it.

The invention relates to a hydraulic circuit for a hydraulic excavatorhaving a motor drive which acts on at least two closed drive circuitswhich are connected in parallel, each have a hydraulic pump and ahydraulic motor and which operate on a common output drive, connectinglines being provided between the hydraulic pump and the hydraulic motorof a respective drive circuit.

The invention further relates to a hydraulic circuit for a hydraulicexcavator having at least two motor drives, each of which acts on atleast two closed drive circuits which are connected in parallel and eachhave a hydraulic pump and a hydraulic motor, in each case two drivecircuits forming a drive circuit group and all the drive circuit groupsbeing connected in parallel and operating on a common output drive,connecting lines being provided between the hydraulic pumps andhydraulic motors of a drive circuit group.

Hydraulic circuits of this type are used, for example, in hydraulicexcavators which have a rotatable upper chassis which is arranged on aslewing ring and is driven by a hydrostatic drive. The hydrostatic drivehas a hydraulic pump which is arranged on a motor drive (diesel orelectric motor), as well as a hydraulic motor which engages in theslewing ring either directly or via a reduction gear mechanism and thuseffects the rotation of the upper chassis.

Small machines are normally provided with an open hydraulic circuit,which effects the change of direction via a control slide. In contrast,larger machines have a closed hydrostatic drive circuit, in which thedirection of rotation and the speed of rotation are controlled byadjusting the pump pitch angle. In many cases, two or more closedhydrostatic drive circuits are provided for design reasons, thesecircuits engaging jointly with their output drive shaft in the slewingring, that is to say operating on a common output drive.

In the case of machines having at least two motor drives, each motordrive may have at least two hydrostatic drive circuits, for example inthe case of large excavators. Machines of this type normally have thedrive circuits connected in such a way that it is possible to operatewith different rotational speeds of the motor drives or with only onemotor drive, while the other is switched off, for whatever reasons. Thehydrostatic drive circuits of known hydraulic circuits of this type areat present connected to one another using lines in order to producebalancing of the pressure, and hence the loading, between the drivecircuits. Furthermore, common flushing and feed systems are provided, aswell as common drive valves for the pump control system.

This type of hydraulic circuit has the disadvantage that, in the eventof damage to a single hydrostatic component in one drive circuit, allthe drive circuits which are connected to one another via connectinglines are infected with particles, so that a large number of hydrostaticcomponents can be damaged as a consequence.

It is therefore already known to provide filter arrangements in therespective hydrostatic drive circuit, these being connected into therespective return to the pump via a non-return valve combination, withthe objective of filtering out the particles. However, this filterarrangement is complicated, since it is necessary for each drive circuitand does not provide absolute security, since there are still manyconnections between the drive circuits, such as those for flushing, feedand control.

The object of the invention is to improve hydraulic circuits of thegeneric type and having one or more motor drives in such a way thatmutual contamination of the components of different drive circuits ordrive circuit groups with particles in the event of damage is largelyavoided, and also ascertaining the damage is simplified.

This object is achieved, in a hydraulic circuit having one motor drive,by the features of patent claim 1 and, in a hydraulic circuit having atleast two motor drives, by the features of patent claim 2.

According to the invention, complete isolation is thus provided betweenthe drive circuits or drive circuit groups, that is to say there are noconnecting lines at all between different drive circuits or drivecircuit groups. The result of this is that, in the event of damage, theeffects of the damage are limited to only one drive circuit or to onlyone drive circuit group, but the other drive circuits or drive circuitgroups are not affected by the damage. In this case it is not possibleeither for the damage to be propagated via the control valves or theirconnecting lines, since each drive circuit or each drive circuit groupis assigned its own control valve. Accordingly, in the event of damage,in each case a maximum of only one control valve can be damaged. As canbe seen, this configuration also makes it simpler to ascertain thedamage, since damage occurs in only one drive circuit or in one drivecircuit group, at least damage with one and the same, and can thus belocated more easily.

In order further to limit the effects of damage in a hydraulic circuithaving at least two motor drives and, accordingly, at least two drivecircuit groups, provision is advantageously made for filters to bearranged in each case in the connecting lines between the drive circuitsof a drive circuit group. Thus, if damage occurs in a hydrostaticcomponent of a drive circuit of a drive circuit group, these additionalfilters make it largely possible to avoid this damage being propagatedfrom the affected drive circuit into a different drive circuit of thesame drive circuit group.

Furthermore, provision is quite specifically advantageously made foreach motor drive to act in each case only on one drive circuit of arespective drive circuit group. Each motor drive thus acts in each caseon only one drive circuit of each drive circuit group, so that even inthe event of failure or stoppage of a motor drive, the at least oneother motor drive in each case drives at least one drive circuit of eachdrive circuit group, that is to say in the event of failure of a motordrive, all the drive circuit groups are nevertheless serviceable withincertain limits.

The invention is explained below by way of example using the drawing, inwhich:

FIG. 1 shows a circuit diagram of a hydraulic circuit according to theinvention having one motor drive and two drive circuits, and

FIG. 2 shows a hydraulic circuit according to the invention having twomotor drives and two drive circuit groups each having two drivecircuits.

FIG. 1 illustrates, as an example, a hydraulic circuit for a hydraulicexcavator for driving the slewing ring of the upper chassis of thishydraulic excavator. This slewing ring of the upper chassis is denotedby the reference symbol D and thus forms the output drive from thehydraulic circuit. The hydraulic circuit itself has a motor drive M; inthis case this may be a diesel or electric motor, for example.

The motor drive M acts on two drive circuits A1 and A2, which areconnected in parallel, each operate jointly on the slewing ring D andare closed drive circuits.

The drive circuit A1 has a pump P1 which is acted on by the motor driveM and is connected via connecting lines L11 and L12 to a hydraulic motorHM1 having a brake B1. On the output side, this hydraulic motor HM1engages via a reduction gearbox U1 in the slewing ring D of thehydraulic excavator.

The second drive circuit A2, connected in parallel, is built up in thesame way. It has a hydraulic pump P2, which is acted on by the motordrive M. This hydraulic pump P2 is connected via connecting lines L21and L22 to a hydraulic motor HM2, which is likewise equipped with abrake B2. On the output drive side, this hydraulic motor HM2 engages viaa reduction gearbox U2 in the slewing ring D of the hydraulic excavator.

In order to control the drive circuits A1 and A2, each drive circuit isseparately assigned its own control valve S1 and S2, respectively, thecontrol valve S1 for the drive circuit A1 being connected via controllines SL11 and SL12 only to the drive circuit A1, while the controlvalve S2 is connected via control lines SL21 and SL22 only to the drivecircuit A2. The control valves S1 and S2 are each connected in a knownway to a common manual control lever H.

As can be seen, the two closed drive circuits A1 and A2 are completelyisolated from each other. If damage then occurs in a hydrostaticcomponent of one drive circuit, the possibility is then ruled out thatparticles released by this damage could pass into the other drivecircuit and could also damage components there. Since the drive circuitwhich is not affected by the damage is thus not impaired, theserviceability of the hydraulic excavator is maintained, naturallywithin limits.

FIG. 2 illustrates a hydraulic circuit for a hydraulic excavator havingtwo motor drives M1 and M2. This hydraulic circuit has two drive circuitgroups AKG1 and AKG2, which are connected in parallel and each of whichoperates on a common output drive, namely on the slewing ring D of theupper chassis of a hydraulic excavator. In this case, the first drivecircuit group AKG1 comprises a drive circuit A11 and a drive circuit A12connected in parallel, while the drive circuit group AKG2 comprises adrive circuit A21 and a drive circuit A22 connected in parallel.

As in the exemplary embodiment according to FIG. 1, each drive circuithas in each case a hydraulic pump which is driven by a motor, and ahydraulic motor with a brake, the respective hydraulic motor operatingvia a reduction gearbox on the common slewing ring D. Theseabove-mentioned hydraulic components are in this case designated in thefollowing way in the drawing:

The drive circuit A11 has a hydraulic pump P11 and a hydraulic motorHM11 with a brake B11 and reduction gearbox U11. In this case, thehydraulic motor HM11 and the pump P11 are connected to each other viaconnecting lines L111 and L112, and the pump P11 is driven by the motordrive M1.

The drive circuit A12 of the first drive circuit group AKG1 has ahydraulic pump P12 and a hydraulic motor HM12 with a brake B12 and areduction gearbox U12 on the output drive side. In this case, thehydraulic motor HM12 and the hydraulic pump P12 are connected to eachother via connecting lines L121 and L122, and the pump P12 has a driveconnection to the motor drive M2.

The drive circuit A21 of the second drive circuit group AKG2 has ahydraulic pump P21, a hydraulic motor AM21 with a brake B21 and areduction gearbox U21. The hydraulic motor HM21 and the hydraulic pumpP21 are connected to each other via connecting lines L211 and L212, andthe hydraulic pump P21 is driven by the motor drive M1.

The drive circuit A22 of the second drive circuit group AKG2 has ahydraulic pump P22 and a hydraulic motor HM22 with a brake P22, as wellas a reduction gearbox U22. The pump P22 and the hydraulic motor HM22are connected to each other via connecting lines L221 and L222, and thehydraulic pump P22 is driven by the motor drive M2.

Balancing lines with filters are in each case provided between the drivecircuits of a drive circuit group. Between the drive circuit A11 and thedrive circuit A12 of the drive circuit group AKG1, these balancing linesare designated by AL11 and AL12, and the filters are correspondinglydenoted by F11 and F12. In the case of the drive circuit group AKG2, thebalancing lines are designated by AL21 and AL22, and the filters by F21and F22.

The hydraulic pumps of each drive circuit group each has its own controlvalve, the control valve of the drive circuit group AKG1 beingdesignated by S1 and the control valve of the drive circuit group AKG2being designated by S2. Both control valves S1 and S2 can be operatedvia a manual control lever H. Each control valve S1 and S2 isrespectively connected via control lines only to its own drive circuitgroup, the control valve S1 to the drive circuit group AKG1, namely viacontrol lines SL11 and SL12, and the control valve S2 to the drivecircuit group AKG2 via control lines SL21 and SL22.

It can be seen from the hydraulic circuit described above that theconnecting lines of each drive circuit group are arranged only betweenthe hydraulic pumps and the hydraulic motors of the respective drivecircuit group, but there is no hydraulic connection of any type betweenthe different drive circuit groups AKG1 and AKG2. In addition, asdescribed above, each respective drive control group has its own controlvalve connected to it. There is thus complete isolation between the twodrive circuit groups, so that in the event of damage in one drivecircuit group, particles which are released as a result of the damagecannot get into the hydraulic components of the other drive circuitgroup. Furthermore, as a result of filters having been provided in thebalancing lines between the drive circuits of a respective drive circuitgroup, it is also largely reliably ensured that particles released inone drive circuit cannot get into the hydraulic components of the otherdrive circuit of the same drive circuit group.

Finally, the cross-coupling according to the invention of the motordrives M1 and M2 in each case to only one drive circuit of a respectivedrive circuit group ensures that the hydraulic drive still operates,within certain limits, even when one motor drive fails.

The invention is of course not restricted to the exemplary embodimentsillustrated. Further refinements are possible without leaving the basicidea. Thus, the exemplary embodiment according to FIG. 2 can betransferred in a similar way to a hydraulic circuit which has more thantwo motor drives.

1. A hydraulic circuit for a hydraulic excavator having at least twomotor drives, each of which acts on at least two closed drive circuitswhich are connected in parallel and each has a hydraulic pump and ahydraulic motor, in each case two drive circuits forming a drive circuitgroup and all the drive circuit groups being connected in parallel andoperating on a common output drive, connecting lines being providedbetween the hydraulic pumps and hydraulic motors of each drive circuitgroup, wherein the connecting lines (L111, L112; L121, L122; L211, L212;L221, L222) of each drive circuit group (AKG1, AKG2) are arranged onlybetween the hydraulic pumps (P11, P12; P21, P22) and the hydraulicmotors (HM11, HM12; HM21, HM22) of the respective drive circuit group(AKG1, AKG2), in such a way that there is no hydraulic connectionbetween the different drive circuit groups (AKG1, AKG2), the respectivedrive circuit group (AKG1, AKG2) each having its own control valve (S1,S2) connected to it.
 2. The hydraulic circuit as claimed in claim 1,wherein filters (F11, F12; F21, F22) are in each case arranged in theconnecting lines (AL11, AL12; AL21, AL22) between the drive circuits ofone (A11, A12; A21, A22) drive circuit group.
 3. The hydraulic circuitas claimed in claim 1 wherein each motor drive (M1, M2) acts in eachcase on only one drive circuit of a respective drive circuit group(AKG1, AKG2).
 4. The hydraulic circuit of claim 2, wherein each motordrive acts only on one drive circuit for a respective drive circuitgroup.